Actually if you already have
a decent normal flatbed scanner you can archive your collection quickly
by scanning many cards in each go, and using a program like RansenScan
to automatically extract and straighten them:

It does not always work the
first time, and you may have to play with the settings:

and maybe use a black background
under the scanner lid, but it certainly speeds up the scan process.

For very faded black and white
(or monochrome) cards the automatic contrast enhancement is a time savng
boon:

You can either set this options
as default, or you can change it on the sub image right after the scan:

So you see you do not need
to buy a new scanner, you can try out the demo of RansenScan (for Windows
8, 7, Vista, and XP) by clicking on the button below